Lecture 01: First Line of Defense: Immunology Basics [SEQ 1]

Study Notes

First Line of Defense

Physical Barriers:
- Skin: A multi-layered barrier. The outer layer (epidermis) contains dead keratinocytes, providing a physical block to pathogens. The dermis, beneath the epidermis, includes immune cells. Skin's acidity (slightly acidic pH), high salt concentration, dryness, and constant shedding all impede microbial growth. Skin-produced antimicrobial peptides (AMPs) further contribute to defense.
- Epithelial Linings: Mucous membranes and cilia in the nose, throat, and intestines create a physical barrier, trapping and expelling pathogens. Coughing, sneezing, vomiting are expulsive reflexes and mechanisms for removal of foreign material.
- Normal Microflora: Naturally occurring bacteria on skin and in the gut help prevent colonization by harmful pathogens.
Chemical Barriers:
- Low pH: Stomach acid (low pH) and skin acidity inhibit microbial growth. High salt concentrations in sweat also inhibit microbial growth.
- Enzymes: Lysozymes, found in saliva and tears, target peptidoglycan causing bacterial cell walls to be damaged, resulting in osmotic pressure damage and bacterial death
- Antimicrobial Peptides (AMPs): Skin, saliva, and other secretions contain AMPs like psoriasin, defensins, and lactoferricin. These peptides target bacterial membranes, disrupt their function, sequester essential nutrients, and ultimately kill bacteria or inhibit growth.
Psoriasin: Damages bacterial membranes by disrupting them, targeting Gram-negative bacteria selectively.
Defensins: Form pores in bacterial membranes, further leading to bacterial death. alpha-defensins are produced in immune cells while beta-defensins are found in skin and saliva.
Lactoferrin: Binds iron, depriving bacteria of this essential nutrient.

Innate Immunity

Innate immunity is a rapid, non-specific response.
Includes macrophages, natural killer (NK) cells, and dendritic cells.

Acquired Immunity

Acquired immunity is specific and long-lasting, involving B cells and T cells.

Description

Explore the essential physical and chemical barriers that serve as our body's first line of defense against pathogens. This quiz covers the skin's protective role, epithelial linings, and the importance of normal microflora. Test your understanding of how these defenses work to keep us healthy.